The COSMOS Magazine article First mission to Mars: Mariner 4’s special place in history July 14, 1965, forever changed the way we see Mars. Tim Wallace looks back at one of NASA’s greatest triumphs recounts some of the excitement that NASA scientists and engineers must have felt during:

...humanity’s first up-close encounter with the Red Planet on July 14, 1965, when the pioneering Mariner 4 spacecraft took the first detailed photographs of the Martian surface, paving the way for future missions to successfully land a probe on the ground.

Remember, this is several years before the first Moon landing!

The article shows several views of Mariner-4, and this one reminds me of an old slide projector both because of what looks to be the central lens (is that Mariner's camera?) and what looks like louvers or air vents on either side.

Question: What are the structures on either side in this image, that look like louvers or air vents? What is their function?

The Mariner 4 spacecraft

The Mariner 4 spacecraft

above x2: Cropped from image in COSMOS Magazine. "The Mariner 4 spacecraft. CREDIT: NASA / JPL"

  • $\begingroup$ Related: space.stackexchange.com/questions/15306/… $\endgroup$ Commented Apr 8, 2018 at 10:33
  • $\begingroup$ @OrganicMarble I'm not so sure that these structures on the side of Mariner-4's are actually louvers or vents. But thanks for the link, I remember that one now :-) $\endgroup$
    – uhoh
    Commented Apr 8, 2018 at 10:36
  • $\begingroup$ Aren't they temperature control devices on both spacecraft? Just one spins and the other louvers open, to control the amount of heat rejected? $\endgroup$ Commented Apr 8, 2018 at 10:39
  • $\begingroup$ @OrganicMarble r.e Mariner 4 I just don't know either way yet. The large and yet flat apertures shown in your link expose the surface to almost 2π of space, whereas louvers are restrictive and have a preferred, more narrow direction of exposure to space, so they would be less effective. I want to wait until I can read further. $\endgroup$
    – uhoh
    Commented Apr 8, 2018 at 11:44
  • 1
    $\begingroup$ Lets see if we can get @prakhar to up their game with some better links etc. Their answer is right just not well supported. $\endgroup$ Commented Apr 8, 2018 at 12:22

3 Answers 3


After some googling, you were indeed right it is Temperature control louvers.

Louver labelled

More detailed labelling for mariner 5 is in this image Not Mariner 4

These louvers control temperature inside the spacecraft. It is a passive temperature control system. Spacecraft Thermal Control

Accordingly, it seems that circular thing is a thruster Mariner 4

Detailed labelling Mariner 4

Image credits : NASA/JPL-Caltech

Image source : m.caltech.edu

  • $\begingroup$ Added, it seems it is a thruster $\endgroup$
    – zephyr0110
    Commented Apr 8, 2018 at 10:12
  • $\begingroup$ Added image source and credits. The credit obviously belongs to NASA/JPL. Thanks for guiding. $\endgroup$
    – zephyr0110
    Commented Apr 8, 2018 at 11:34
  • $\begingroup$ If you look at almost all other answers in this SE site which have images, you will see that people add links directly to the sources of each image. $\endgroup$
    – uhoh
    Commented Apr 8, 2018 at 12:03
  • 2
    $\begingroup$ @Prakhar it's actually considered passive thermal control despite the moving parts. No cooling loop. nasa.gov/feature/goddard/2016/… $\endgroup$ Commented Apr 8, 2018 at 12:10
  • 1
    $\begingroup$ @organic Yes, it indeed looked like passive to me. I was misguided by the article saying " Active Thermal control components include louvers ". I misinterpreted as the system though it was talking about components. $\endgroup$
    – zephyr0110
    Commented Apr 8, 2018 at 12:47

I just ran across the louvers in close-up view!

In the JLP video 1965: Discovery at Mars there is an excellent video The Changing Face of Mars with introductory remarks by its producer/director/writer, Blaine Baggett, Director, Office of Communication and Education, JPL, about Mariner 3 and 4 missions to Mars embedded within his Von Karman lecture.

At about 00:38:50 you can see them "moving" (could be Mariner 3 or 4):

Mariner 4 thermal louvers


They are, in fact, called louvers, and they are for thermal control. Under the louver is a radiator designed to reject waste heat efficiently. When the louver is open, the radiator has a good view of cold space and dumps heat. But close the louver, and the heat rejection drops substantially. Louvers are used when the spacecraft has heat sources which vary dramatically with time. I worked on the Dawn spacecraft, launched in 2007, and we used louvers. In Dawn's case, the ion propulsion system used gobs of power and, since it wasn't 100% efficient, it also generate lots of waste heat. When it was running, the louvers were wide open to reject that heat and prevent it from overheating the rest of the spacecraft. Turn off the ion propulsion system, and the lovers closed - kind of like zipping up your winter coat. The diagram below shows the location of the louvers on Dawn.

Louvers are passive devices which require no commands or motors to open and close. They use a bimetallic strip like a thermostat to turn temperature changes into (small) forces which, in zero g, are enough to open and close the louvers.




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